Russia's Progress M-16M (48P) cargo craft will lift off atop a Soyuz-U booster from the Baikonur Cosmodrome, Kazakhstan on Wednesday, Aug. 1 and arrived at the International Space Station six hours later.

With this launch, Russian mission controllers are testing a modified rendezvous plan designed to reduce the typical two-day flight to the ISS. If applied to the crewed Soyuz vehicles, this would increase crew comfort and provide for additional contingency time at the end of the spacecraft’s mission.

apolloprojeckt

That is great. How long do they know this other way quicker docking? This must be a substantial cost reduction yield and extra risk.

Jay Chladek

Technically one day missions from launch to docking were possible with the Soyuz craft from day one going back to the Salyut days. When the ferries were redesigned after Soyuz 11, they lost the solar arrays and were equipped with storage batteries (partly as a weight savings measure due to the added mass they needed to carry for the life support systems and pressure suits), which meant that they had a limited lifespan in orbit before having to come home. So a one day flight to the station was preferable. If the docking didn't occur within a certain period, the Soyuz would have to come home. The Soyuz T series brought back the arrays and the power restrictions were loosened since longer independent flight was again possible.

The low fuel consumption trajectories used by the Progress craft starting with Salyut 6 were first tested on the Soyuz T craft if I remember correctly and the Soviets opted to go with that slower rendezvous path for the Progress modules since it had less chance for error and burned less fuel (which would allow for more fuel to be pumped into the fuel tanks of the Salyut for reboost operations).

Just remember that at the time Progress started flying (early 1980s) automated dockings were still a relatively new thing. The US systems used for Apollo and Skylab (plus Gemini) had helped to automate part of the rendezvous process with mission control on the ground updating things in near realtime. But it was still up to the astronauts to acquire the target visually and fly the last part of the docking. The same was true with the Soyuz/Salyut dockings in those early days.

The Soyuz craft began utilizing the longer approaches as well for similar reasons (more fuel for docking attempts), since they weren't as limited in their on orbit life as the early ferries. The TM series introduced a new Argon computer that could fly a completely automated rendezvous approach and docking with no input from the crew or the ground if everything worked properly. But the designers preferred to have it flying a Progress path as opposed to something closer to what the early approaches utilized, hence two day flights to stations instead of one.

I believe part of the reason why the slower rendezvous trajectories with Progress continued to be used had to do with a lack of funding. The Igla was the first rendezvous system and then it was replaced by the first Kurs system introduced on Mir. We might have seen a more advanced Kurs come about sooner if the Soviet Union had not fallen since the factory that made the original system is based in the Ukraine. After Ukraine became independent, the price they were charging for Kurs went up.

The financial problems suffered by the Russian space program over the next several years meant that they didn't have the money to support R&D for a more advanced Kurs. There were also some bugs that cropped up in the Kurs as well late in Mir's life (some of which were factors in the near miss and collision incidents) and I imagine a bit of money and time had to be spent making the system more reliable for the ISS flights before work could commence or continue on a newer generation Kurs.

Robert Pearlman

While advancements to the navigation system is a factor in the new "expedited rendezvous," the change is due more to orbital mechanics then it is technology, as Jim Oberg explains in his article for IEEE Spectrum:

...but there is a second, less well-known launch window that has been the primary driver behind a standard two-day (sometimes three-day) rendezvous. It is connected to the awkward fact that at the precise moment the spacecraft must launch to hit the right orbital plane, the target satellite can be anywhere along its near-circular, approximately 92-minute-long orbit around Earth. The difference in the position of the spacecraft and target along the same track is called the phase angle.

You make up for the phase angle by launching into a lower orbit, which has a speed slightly greater than that of the target. As the chasing vehicle climbs into the target’s orbit, it closes the distance between them. The lower the initial orbit, the faster the chaser catches its target.

With two days to catch the space station, you’ve got a lot of choices for your initial altitude, a wide range of possible overtaking speeds, and therefore a big choice of phase angles to work with. According to Murtazin's recent paper, Soyuz can catch the ISS as long as it gets anywhere within 42 percent of the station's entire orbital arc (about 150 degrees). This gave Russia's space agency opportunities to launch as often as every other day.

But for the fast rendezvous, there is a greatly diminished capability to overtake the station. Even with the most recent tweaks to the plan, less than 6 percent of the orbital arc is accessible.

Waiting for the right slot is frustrating — weeks could go by between opportunities. So throughout July, the station's orbit has been gently tweaked, with rocket firings to nudge it into the sweet slot for Kazakhstan launches...

jasonelam

How long was the launch window for the launch? Seems like it was instantaneous.

SkyMan1958

Does anyone know how the liquid supplies, e.g. propellant and oxygen/nitrogen are transferred from a Progress vehicle to the ISS? Are they basically tanks that a hose is hooked to the receiving tank on the ISS? Thanks.